ABSTRACT. The paper deals with the distribution pattern and population dynamics of the introduced barnacle Balanus glandula in the intertidal areas of Mar del Plata port. The reproductive cycle of this barnacle is discussed as a community structuring force. Replicated areas in both the high intertidal and the upper mid intertidal zones were monthly denuded. The recruitment, cumulative settlement, mortality and growth of B. glandula were recorded, as well as the succession pattern of the associated fauna. First settlement of B. glandula occurred in winter (July). Succession begins with a film of microorganisms followed by green algae (Ulvalactuca and Enteromorpha spp.) which dominate up to a final stage of B. glandula dominated community is reached all along the intertidal. B. glandula densities were significantly higher in the mid intertidal than in the high intertidal (19600 and 13600 ind. m-2, respectively). Annual mean mortality was high in the port (up to 62%) but heavy settlement allowed a final density 4 times greater than in the upper mid intertidal of exposed rocky shores, and twice the greatest density reached in the Northern Hemisphere. Winter reproduction of B. glandula, absence of predators, and the neutral or beneficial effect of algae allows this species to occupy in wave protected areas the whole intertidal zone, displacing the former B. amphitrite populations from the intertidal to the subtidal. In exposed rocky shores the species outcompete mussels from the high intertidal, establishing the typical barnacle fringe